Microsoft seems to have decided to entirely break this expectation such that closing the lid of a laptop puts it into this weird not-really-suspended state, such that putting it in a confined space could cause it to overheat. It's... pretty user-unfriendly and IMO stupid.
Ultimately the company selling to the end user has to stand over the package they're selling.
Closing the lid does not necessarily turn the laptop off at all (by design). I think most people have had that experience. In fact the lid may be closed with the laptop fully on.
In any case, they make is explicit and clear exactly to avoid any such assumption.
The title is obviously clickbait because of course you can put your Dell laptop in a bag and of course that does not void the warranty.
Weird that you're angrier about a headline than a warranty being voided by putting a laptop in a bag.
Or in other words, from the perspective of the hardware, what is about to happen once somebody closes the lid?
The fault lies with Microsoft, mismanaging the user expectations about shutting down the computer.
The computer should absolutely not wake up from sleep to do things, if the result could be that it overheats. It's like saying people shouldn't pocket their smartphones.
What they actually say: "Under no circumstances should you leave a laptop powered on and in any sleep/hibernate/standby mode when placed in a bag, backpack, or in an overhead bin. The PC will overheat as a result of that action. Any resulting damage will not be covered by the Dell warranty."
Fair enough. A laptop that overheats because it's been left in an enclosed space whilst not off is not damage caused by a fault of the device.